1. Field of the Invention
The present invention relates to a controlling system and method for controlling an audio or video unit by using a computer.
2. Description of the Prior Art
When an audio or video unit for example a VTR unit was controlled by using a computer, it was difficult to electrically connect the control terminals of the VTR unit and those of the computer. As an intrinsic matter of VTR units, when two or more VTR units were used for editing a program, timings of these VTR units should be precisely matched. Thus, in this situation, a dedicated controller was sometimes used.
As an example, in an editing system including a reproducing VTR unit and a recording VTR unit, a magnetic tape recorded both video information and a time code for representing the position thereof. The editing controller received a time code reproduced from each VTR unit and generated a control signal for controlling an operation mode of each VTR unit. In this situation, the editing controller controlled each VTR unit so that a particular operation mode was executed at a particular timing. As a result, after both the VTR units were in a synchronous operation state, the recording VTR unit recorded a reproduced output of the reproducing VTR unit.
The applicant of the present invention has proposed a system having a clocking means for sharing the same time among a controller and audio or video units controlled thereby so that VTR units can be controlled by a personal computer. In this system, a communication protocol referred to as VISCA protocol was used among the controller (specifically, the personal computer) and the audio or video units. An outline of this communication protocol was in that a command associated with a time of the common clock was sent through two-way communication lines. A receiving unit stored the received command and executed the command at the time specified by the command.
As described above, although the system had a reference time, it was impossible to solve an intrinsic delay of a VTR unit which took place when the unit executed a command. In other words, even if a recording VTR unit released the record pause state at a designated time and started a record operation, this VTR unit had a slight delay in the record operation. As a result, the beginning of the image to be recorded was lost.
The conventional editing controller was provided with a timing adjusting means for solving an intrinsic delay of the unit. In other words, the editing controller sent to the recording VTR unit the record pause releasing command at an earlier time by the measured delay time. As a method for measuring this delay time, a tape which displays a second hand of a clock on a screen was provided. Thereafter, the tape was reproduced and edited so that the position of 0 second was referred to as a cut-in point. Next, the edited tape was reproduced and a deviation of the cut-in point was determined on the screen. This delay time was set as a timing adjustment time of the edit controller. Thereafter, the same edit operation was repeated and the timing adjustment time was set so that no deviation took place.
As described above, when a delay time was measured, a tape which displays a time on the screen was required. Thus, this system required the user to perform a complicated edit operation. In addition, when the timing was finely adjusted, the adjustment became troublesome. Thus, only coarse adjustment such as intervals of 2 sec was available.
In the above description, only an intrinsic delay of the VTR unit was described. However, there is another delay which takes place over a communication line and a VTR unit after the controller sends a command to the VTR unit until the controller receives the reply such as the position of a recording medium (a tape or the like). Thus, this delay results in deteriorating the editing accuracy.